In many construction applications there is a need for measuring building components before they are installed. In this sense, many of the construction components are custom sized or fit into a particular location. This is true for all manner of materials used in a typical construction project. For example, it may be necessary to measure the distance between two walls to determine the required length for a stud wall. Once the stud wall is erected it may be necessary for the builder to measure panels of drywall to cover the surface which may not even be rectangular. In most cases the workers will carry metallic non-disposable measuring tapes which can be used on the job site to make spot measurements of building materials.
However, there are many disadvantages to such steel measuring tapes. While they are quite durable, they are only temporarily placed against the workpiece and then retracted and stored until needed the next time. The act of retracting and storing the tape can result in the person making the measurement forgetting what was measured, requiring the measurement step to be repeated. Additionally for longer spans, it is necessary for two people to be present so that one can hold the far end of the tape onto the workpiece and the other can read off the measurement, or make an appropriate mark on the workpiece for cutting or the like. The need for two people is awkward and labour intensive.
In the past the problems of such steel tape measures have been recognized and various efforts to provide disposable pressure sensitive adhesive backed marking tapes have been made. Such a tape can be stuck onto a workpiece by one person, and left there to provide easy measuring. For example, U.S. Pat. No. 4,351,113 addresses many of the concerns associated with steel tape measures and discusses a number of criteria for adhesively backed measuring tapes. These include accuracy, tensile strength, adhesion strength, markability, elasticity, and cost. To meet these criteria the patent teaches a tape made from a creped paper base which has a fibrous organic nature. In this manner the tape of this invention is susceptible to stretching forces to conform to small irregularities in the surface to which it is applied, without wrinkling or changing direction.
While there are certain advantages to the invention taught by this prior patent the disadvantages are significant. Most particularly there is a concern with accuracy. Although creped paper of the sort described will allow some stretching to accommodate surface irregularities, is also not dimensionally stable. Depending upon how much tension is applied to the tape at the point of application to any surface the tape will stretch to a greater or lesser extent. Any grid printed on the tape will also stretch. This causes measurements based upon the grid of the tape to be off. If the measurements are not accurate, they might just as well not be made at all. The patent attempts to address this by printing a set of false indicia which when stretched by the average person will become dimensionally correct. Unfortunately this is impractical in practice as not everyone will use the same force to lay the tape, nor is it even likely that a single person will use the same force in laying out the tape at different times during the same day.
Another problem facing printed tapes are to form a good set of reference or measurement marks on the upper surface. Conventional tapes are impregnated with a release agent to facilitate the easy unwinding of a length of tape from a roll. Without a release agent on the upper surface, the tape adhesive will stick to the upper surface causing the tape to rip or tear rather than coming cleanly free. Unfortunately, application of the release agent can interfere with the printing ink being able to set to the tape surface. There is a tendency for the image to bleed or to lift off with the overlying adhesive layer. Either event can cause the markings to be obliterated rendering the tape virtually useless for measuring purposes. This problem was addressed in U.S. Pat. No. 4,599,260, where the patent teaches applying an adhesive to one face of the tape and a low adhesion backside coating and an ink adhesion promoter to the other face. Unfortunately this requires a number of manufacturing steps and is awkward to reliably implement.
Other printed tapes have been proposed, with various types of markings, but none have met with commercial success. Examples of these prior patents include: U.S. Pat Nos. 4,708,755; 4,845,858; 4,942,670; 5,012,590: and 5,107,601. Each of these prior patents teaches a tape which attempts to overcome the problems, but none of them have met the concerns of the marketplace.